"Climate tech startup Silicate is set to start the first-ever enhanced weathering trial in the United States. The trial will involve applying 500 metric tons of milled returned concrete to 50 hectares of farmland in Buckingham, Illinois. According to company estimates, this project has the potential to remove as much as 100 tons of carbon dioxide from the atmosphere annually."
Enhanced Weathering, as the practice is called, has merit and is being investigated by a dozen startups. The idea of spreading Olivine (a magnesium iron silicate) or Brucite (magnesium hydroxide) or Wollastonite (calcium inosilicate) has been floated around for a while.
There are three aspects relating to its feasible application - as distinct from theoretical considerations.
1. Is the process feasible?
The slow reaction rate seems to be a significant obstacle. Additionally, these minerals are rarely pure and may vary significantly in quality from source to source, leading to a QA/QC problem.
2. Can the process be scaled-up?
Contrary to earlier comments, there is no wide availability of these minerals, not at the scale needed to make an impact. Moreover, the material-handling side of the issue is not well addressed. It isn't a simple question of drawing a distribution network on a diagram: it's working out the economics of the mass mining, transport, distribution and application of these materials. People are working on this, but I have not yet heard a compelling solution.
3. Are there undesirable side reactions?
This is what farmers will worry about. It'll be good if these amendments increase soil fertility, but that has to be demonstrated. Do these amendments alter the physical structure of soils or reduce their capacity to retain water, especially after carbon is absorbed? Do they form concretions over time that would make soils less permeable? Does the exposure to plant exudates release contaminants in soil?
I was involve in a project at a Canadian diamond mine in which the host rock - Kimberlite - absorbed CO2. This caused a decrease in its alkaline pH and allowed small quantities of sulphides to oxidize and release contaminants. Clearly, this is the kind of undesirable outcome that must be avoided.
Lots more to say, but perhaps some EW experts will chime in.
This whole 'undesireable side reactions' thing is completely overblown for basalts. The effects to soil of volcanic ash from eruptions is quite well studied, not to mention crushed basalt is a recognised fertiliser in organic and biodynamic farming, and there have been places spreading it each year for the last 40 years (purely as a fertliser). You cant use rocks with significant sulphides or other heavy metals though, that has to be tested before spreading. Basalt is quite wide spread.
"Climate tech startup Silicate is set to start the first-ever enhanced weathering trial in the United States. The trial will involve applying 500 metric tons of milled returned concrete to 50 hectares of farmland in Buckingham, Illinois. According to company estimates, this project has the potential to remove as much as 100 tons of carbon dioxide from the atmosphere annually."